Controllable Filler Prefloculation Using A Dual Polymer System - Patent 8088213

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Controllable Filler Prefloculation Using A Dual Polymer System - Patent 8088213 Powered By Docstoc
Description: STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not Applicable.BACKGROUND OF THE INVENTION This invention relates to the preflocculation of fillers used in papermaking, particularly, the production of shear resistant filler flocs with a defined and controllable size distribution at high filler solids is disclosed. Increasing the filler content in printing and writing papers is of great interest for improving product quality as well as reducing raw material and energy costs. However, the substitution of cellulose fibers with fillers like calcium carbonateand clay reduces the strength of the finished sheet. Another problem when the filler content is increased is an increased difficulty of maintaining an even distribution of fillers across the three-dimensional sheet structure. An approach to reducethese negative effects of increasing filler content is to preflocculate fillers prior to their addition to the wet end approach system of the paper machine. The definition of the term "preflocculation" is the modification of filler particles into agglomerates through treatment with coagulants and/or flocculants. The flocculation treatment and shear forces of the process determine the sizedistribution and stability of the flocs prior to addition to the paper stock. The chemical environment and high fluid shear rates present in modern high-speed papermaking require filler flocs to be stable and shear resistant. The floe size distributionprovided by a preflocculation treatment should minimize the reduction of sheet strength with increased filler content, minimize the loss of optical efficiency from the filler particles, and minimize negative impacts on sheet uniformity and printability. Furthermore, the entire system must be economically feasible. Therefore, the combination of high shear stability and sharp particle size distribution is vital to the success of filler preflocculation technology. However, filler flocs formed by a low molecular weight coagul